1. Field of the Invention
The present invention relates to an echo removing system, and in particular to an improved echo removing system which makes it possible to more effectively remove echoes which occur during a wireless communication between a mobile communication subscriber and a fixed communication subscriber in a code division multiple access (CDMA) type mobile communication exchange system.
2. Description of the Conventional Art
Generally, in the CDMA type mobile communication exchange system, during a wireless communication between a mobile communication subscriber and a fixed communication subscriber, an audio signal of the mobile communication subscriber is transmitted to the fixed communication subscriber through the mobile communication exchange system and a public switched telephone network (PSTN) which is a public analog telephone network for an audio signal transmission, respectively. During this communication operation, the echo occurs due to a mismatch of a hybrid impedance of lines 2 and 4 of a matching section of the fixed communication subscriber. The audio signal is delayed by about 180 msec due to a voice coding of a base station controller (BSC) of a public land mobile network (PLMN).
When this delayed audio signal is outputted to the mobile communication subscriber, the mobile communication subscriber may hear his/her echoed voice after speaking, for causing inconvenience when communication takes place between the mobile communication subscriber and the fixed communication subscriber.
Therefore, it is necessary to remove the echo which occurs in the matching section between the mobile communication subscriber and the fixed communication subscriber for enabling a quality communication therebetween.
When all the access subscriber subsystems (ASS) having an echo removing system may remove the echo by controlling the echo removing system, removing the echo may be made easier and simpler.
However, if all the ASSes are removed in such manner, the communication quality is degraded, and the echo removing system has to be disadvantageously installed, all the ASSes then requires the echo removing system as well.